ARM Architecture

10 Circuit Parts You Ought to Know


Cooks have their miscellaneous components, like condensed milk, cream of tartar, and xanthan gum. As engineers, we too have fairly our decide of circuits, and a very good circuit designer ought to know what’s on the market. Not simply the bread and butter components like resistors, capacitors, op-amps, and comparators, however the miscellaneous “gadget” elements as nicely.

Listed here are ten circuit elements chances are you’ll not have heard of, however that are often fairly helpful.

1. Multifunction gate (74LVC1G97 and 74LVC1G98)

7400 collection logic has undergone a metamorphosis over the previous few many years, from elementary logic constructing blocks in 14-20pin DIP packages, to single-gate glue logic in small low-count SOT-23-6 and SC-70-6 packages. TI launched two components that are “multifunction gates” — they’ve an odd reality desk based mostly on 3 inputs that permits them for use as AND gates, OR gates, inverters, buffers, multiplexers, and so forth. relying on how the pins are linked. They’re now second-sourced by Fairchild, NXP, and ON Semiconductor.

Why use these components?

The final circuit design I labored on wanted a number of glue logic components. We might have used 1G04 inverters, 1G32 OR gates, 1G00 NAND gates, and 1G00 AND gates. As an alternative, we used 1G97s and 1G98s. We wanted to retailer fewer totally different components due to this.

If in case you have a small stash of those two gates obtainable, they’re there in a pinch if you want them.

If I had a manufacturing design with just one NAND gate and no different logic gates, I would use a 1G00: it is cheaper than the 1G97. However in any other case, they’re like a Swiss Military knife for glue logic.

2. TL431 adjustable shunt regulator

If you happen to take a look at the schematic of any isolated-output energy provide, chances are high it makes use of a TL431 and an optoisolator. The TL431 primarily acts like an NPN transistor or N-channel MOSFET however with a precision 2.5V VBE/VGS drop. Within the TL431, the pins are known as cathode (Ok), ref (R), and anode (A). The Ok and A pins are analogous to empty and supply of a MOSFET, and R is analogous to the gate

If that does not imply something to you, consider it as a precision comparator:

When the reference pin is greater than 2.5V above the anode, the half begins to conduct between cathode and anode.

You need to use this as a precision comparator, or as a shunt reference (by connecting a resistor divider throughout cathode/ref/anode pins). In switching energy provides, they’re normally used as a suggestions regulator: a voltage divider connects to the ref and anode pins, with an optoisolator diode linked in collection with the cathode, in order that when the ability provide output reaches its regulation level, the TL431 begins to conduct via the optoisolator, inflicting the ability provide controller to scale back its output. You will normally see a capacitor linked between ref and cathode pins to stabilize the suggestions loop.

There is a wonderful article on designing with TL431s in energy provides by Dr. Ray Ridley.

Many producers have TL431 equivalents, and the components are cheap.

There are additionally a number of “low-voltage” variants just like the TLV431, TS431, and LMV431 which have thresholds of 1.24V slightly than 2.5V. These are additionally helpful, however watch out for the restrictions on cathode-to-anode voltage: the TLV431 and TS431 solely work as much as 6V; if you wish to go increased you might want to use the TLVH431 which matches as much as 18V. The LMV431 works as much as 30V cathode-to-anode voltage. All of those elements have decrease (higher) specs on reference leakage present than the plain TL431 (0.5uA max as an alternative of 4uA; the TS431 has specs of 0.16uA!), and decrease minimal cathode-to-anode working present (60-100uA max as an alternative of 1mA). If I had been utilizing a micropower circuit, I would flip to those components first due to their higher efficiency, though the TL431 is cheaper.

3. Oscillator + multistage counter: 74HC4060

If you must design a 1Hz oscillator with out utilizing a microcontroller, your first intuition is perhaps to make use of a 555 oscillator. It is going to work, however not nicely — when you attempt, you may discover that you simply both have to make use of a really massive resistor or a really massive capacitor. If you happen to use a big resistor (>1 megaohm), the oscillator frequency is liable to variation from leakage present from the 555 or from floor contamination on the circuit board. If you happen to use a big capacitor (>1uF), it could be bodily massive, or costly, or endure from poor tolerance or excessive inside leakage.

A greater method is to make use of a chip just like the HC4060 and a 32.768kHz watch crystal, and never have any of the tolerance problems with an RC oscillator — 32kHz quartz crystals are normally specified at 20ppm accuracy. The 4060 accommodates an oscillator driver (simply an inverter and buffer) and a 14-stage counter. With the oscillator driver, you possibly can drive an RC circuit or a crystal. The counter divides down the enter to lower-frequency outputs, and provides you 10 faucets out of the 14 phases — with 32.768kHz supply frequency, the 4060 yields all power-of-2 frequencies from 2.048kHz right down to 2Hz apart from 16Hz. (You can get 1Hz by taking the 2Hz output and placing it via a flip-flop.)

4. Ceramic resonators

Typically you want a frequency supply that’s extra correct than an RC filter, however doesn’t should be as correct as a quartz crystal.

Ceramic resonators are two-terminal or three-terminal resonators which are about 0.5% accuracy; higher than the 5% best-case accuracy you get from RC filters (capacitors with higher than 5% tolerance are costly), however poorer than the 50ppm or higher you may get from a quartz crystal. The three-terminal selection have built-in capacitors for making certain correct oscillation. The standard frequency vary is 200kHz – 50MHz.

From what I bear in mind, ceramic resonators was cheaper than crystals. I simply checked on Digikey, and this does not appear to be the case anymore — they’re about the identical; barely costlier for floor mount however barely cheaper for through-hole. Ceramic resonators do have one main benefit over crystals: they’re bodily smaller, with 4mm x 2mm dimension as an unusual possibility for SMT ceramic resonators (together with built-in capacitors!), whereas the smallest usually obtainable crystal dimension is about 8.5mm x 3mm.

Ceramic resonators will not be applicable for timekeeping — a 0.5% correct frequency supply might acquire or lose 7 minutes per day! — however one software which might use them is a UART. If in case you have a microcontroller software, the place the one frequency accuracy requirement is speaking over RS232, 0.5% accuracy is a lot. UART bytes with begin and cease bits have 10 bits per byte, so 5% error within the frequency interprets to half a bit per byte, and 0.5% error interprets to 1/20 of a bit per byte. RC accuracy is marginal for this kind of software, however ceramic resonators are wonderful.

5. Switched-capacitor charge-pump inverter (ICL7660 or equal)

To illustrate you’ve a 5V, 1A energy provide and also you’d actually like a -5V provide for one or two analog circuits. Intersil invented a component over 20 years in the past that meets the invoice: the ICL7660.

This half takes an exterior capacitor and alternates switching it between two connection paths. If you happen to make one among these paths the 5V energy provide and the opposite the -5V provide rails, then the capacitor expenses up throughout the 5V provide and discharges throughout the -5V load.

For a number of milliamps, it really works wonderful. Many producers make a 7660 circuit, so there are a number of sources.

However it’s not a regulated energy provide. The output impedance of the 7660 is a operate of the onboard change resistance, the exterior capacitor worth, and the switching frequency. The extra present you draw from the 7660, the extra the voltage will droop in direction of zero.

It is also a switching converter, each drawing and delivering pulses of cost when the capacitor switches, so it produces noise on the switching frequency.

Nonetheless, it is a helpful half to have in your again pocket for that one circuit in your board that wants a detrimental energy provide.

6. Low-voltage differential signaling (LVDS) drivers and receivers

There are numerous schemes for sending serial knowledge between separate units. Most of them use differential signaling. The one main one that doesn’t is RS-232, which has sensible limitations on baud fee if there’s noise current. The others embrace RS-422, RS-485, CAN, and LVDS. These all use differential pairs, so all are far much less delicate to common-mode noise that’s induced on each indicators. LVDS is continuously used to ship digital knowledge between computer systems and screens. It makes use of a lower-voltage sign swing than the degrees utilized in CAN or RS-485, so the ability utilization and the emitted noise are a lot decrease.

If in case you have indicators you might want to transmit from one circuit board to a different, that want good noise rejection, chances are you’ll want to use LVDS to encode/decode them on every finish. Some examples are SPI or PWM indicators — each are delicate to glitches.

7. I/O expanders

So you’ve got acquired a microcontroller in an software that is nonetheless including new options, and as you add an increasing number of inputs or outputs, you are operating out of pins.

There are chips obtainable that may be managed over I2C or SPI that may deal with less-frequently-changing inputs and outputs. My favourite is the MCP23017 and MCP23S17. These are 16-pin units; the 23017 is I2C and the 23S17 is SPI.

If you happen to want one thing for outputs solely that is cheaper and easier, you may get away with utilizing 74HC595 shift registers on a SPI bus. Every 595 is an 8-bit output that has its inputs shifted in on the SPI clock sign and latched into its outputs on the rising fringe of the CS sign.

8. Excessive-side present sense amplifiers

There are occasions when you must measure the present right into a load circuit and you may’t interrupt the bottom connection. This leaves you with high-side present sensing. There are a number of choices for high-side present sensing:

  • built-in circuits with built-in sensing parts
  • hall-sensor based mostly present sensors
  • present sense resistors + amplifiers

The final of those might be the least costly and most versatile. I just like the ZXCT collection of present sensors launched by Zetex, which was acquired by Diodes Inc. These are used to detect unidirectional currents and produce a present output proportional to the sensed voltage. Their bandwidth is fairly first rate and the quiescent present is within the 2-5uA vary. The concept is that you simply use a collection resistor to show the output present right into a voltage, after which do with it what you want (e.g. buffer it). I attempted investigating numerous various approaches from different distributors in 2008 or 2009, and ended up concluding this was the most effective performing possibility for an inexpensive worth.

They aren’t helpful for bidirectional currents (e.g. charging/discharging batteries) until you utilize two units, one in every path; it is a far more troublesome downside to unravel with one gadget.

9. Present sense resistors

There’s an artwork to selecting present sense resistors. You need a resistor that produces as small a voltage as doable so it does not intervene with the remainder of your circuit… however alternatively, you need one which produces as massive a voltage as doable so your sign is massive sufficient to make use of. It could have to dissipate a number of watts if the present it is measuring is massive, however you need it to be cheap and small. Oh, and it must be correct.

In case your currents are under 100mA, it is not that arduous of an issue to unravel (1%, 1 ohm or 0.5 ohm resistors able to dissipating greater than 10mW will not be very exhausting to search out).

In any other case, chances are high, these might be your primary necessities:

  • 1% accuracy or higher
  • 0.1 ohms or smaller

Listed here are a number of of my favourite present sense resistors:

For currents within the 1-10A vary, you should utilize “common” SMT low-ohm resistors like Panasonic ERJ and Stackpole CSR.

For big currents (>10A), steel parts are a very good match:

10. Analog multiplexers and switches

Typically you might want to change analog indicators, whether or not it is to develop the variety of inputs into an analog-to-digital converter, or select totally different acquire resistors, or one thing else.

I divide the sorts of multiplexers into 4 teams:

A. CD405x / 74HC405x multiplexers and 4066 switches

The usual digital logic collection (CD4000 = 5-15V, 74HC = +/-2-6V) comprise analog switches. The 4051 is an 8:1 analog multiplexer; the 4052 is a twin 4:1 analog multiplexer; and the 4053 is a triple 2:1 analog multiplexer; the 4066 is a quad change. These are cheap and made by a number of producers. However they’ve drawbacks; the leakage present is spec’d at 1uA and the on-resistance normally runs within the tens or low a whole lot of ohms.

B. “Improved” 405x with higher leakage/on-resistance specs

You will want these if in case you have high-impedance inputs or on-resistance is a vital requirement.

Maxim was the primary firm to introduce a pin-compatible collection of switches/multiplexers (MAX4051/2/3) with improved specs (leakage present lower than 0.1uA, on-resistance of

C. Single-switch options with good leakage/on-resistance specs

4157 SPDT change — these are made by a number of producers, are pin-compatible with one another, and have on-resistance within the

Fairchild FSA4157

Vishay DG4157

ON Semi NLAS4157

D. Different

This class contains analog switches with odd voltages or excessive bandwidth necessities or in any other case do not meet the above classes.

The one recommendation I can provide you right here is to have a look at choices from Analog Units, TI, Fairchild, Vishay, and ON Semi.


There are tons of electronics elements on the market — it is essential to maintain up with what’s available on the market.

Most of the producers and distributors ship out new product advertising; Linear Know-how and Texas Devices are among the many most prolific.

Commerce periodicals like EDN and Digital Design are good locations to find out about new merchandise.

One of the simplest ways to be taught what’s on the market, nonetheless, is to search for it. It may be time-consuming, however you may have some new instruments to maintain in your again pocket.

Good luck along with your subsequent circuit design!

p.s. do you’ve a favourite oddball circuit element that is not in my listing? In that case, please submit a remark and let me know.

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