Amplifying a 5V sq wave to 60V


#1

Is there an easy way to get a 60V sq wave from a 5V digital signal.

I’ve got a DIY car ECU that outputs a digital 5V tach signal, the problem is that my tach uses the high voltage coil flyback as a signal and won’t trigger off that.

Currently I have a MOSFET switching a relay with the contact bar removed - too noisy otherwise - , and it’s the flyback off that that makes the tach work.

I don’t know much about actual electronics, but is there any simple ideas I could research. I don’t really know what to search for because I know nothing.


#2

The circuit is the easy part, an npn transistor such as the 2n5551 (160V breakdown) will do it. The input is a resistor from your 5V output port to the base with the emitter on ground. A largish (10K to 50K because you don’t need much current) resistor to a 60v supply on the collector gives you your 60v output. The hard part is a boost regulator to get 5v to 60V. Most of the ebay cheapies are limited to about 30v ouptut. If you can find a cheap one that will do 60v with at 5V input you will be away. I’d be tempted to try it with 30V on the collector from one of the cheap inverters or an external 30v supply and if that works use one of the 3 or 3 dollar inverters from ebay.

edit: found at least one:

its a little large and would need to run of the 12 v supply but it is reasonably cheap way more current than you need as well (which is why so large).

Peter


#3

I am not an EE so what I have to say may be the hard way of doing things but if I needed to do what you are saying I would consider building a HV power supply using a PWM chip with an inductor and large smoothing cap. Then use your transistor to convert the 5V pulses to 60V.

Here is an example of a simple HV power supply made with all through hole components. http://www.smbaker.com/high-voltage-power-supply

If you want to buy a tiny one you can search on eBay for Nixie power supply (My collection). With the nixie ones they will be set to around 170V but it is usually easy to switch the reference resistor to get lower voltages from them. I use tiny transformer based ones like this.


#4

I was just think about a boost converter and switching with a MOSFET.
This is what the working relay and MOSFET are producing, but I don’t know how low I can go.

I have some SEPICs 45V Buck-Boost around here, so I might try that first.


#5

A simple voltage divider such as a 50k or 100k (so it draws little current) pot with the input signal to the top and the wiper to the tach trigger input should let you adjust the voltage to the tach until it reads dependably. That in turn will tell you the minimum voltage you can get away with. Another option I just thought of is a 12 v to 120V power transformer. If you switch the 12v side with 5v you will get around 60v on the 120V secondary side. It probably won’t go that fast though not more than 120 hz or so I don’t think, so you may need to use an audio transformer if you need a couple of khz (which you may for 5000 rpm or so) and finding the turns ratio you need is a bit more complex.

edit: this may do the trick:

at 1:25 about 3V in would give 75V out, so you would probably need a resistor voltage divider on the input to reduce the 5V signal enough to give you the 60v output you need something like 2 1k resistors in series should give about 2.5v at the center of the resistors (or a 2k pot so you can adjust the output voltage) to connect to the input of the transformer and thus 62v out on the output. This is probably the cheapest and smallest solution. It should work up to 5khz or so perhaps more.

Peter