hi friends,
Do you have an idea or circuit for "AC square wave constant voltage generator" with short circuit protection ? The spec: 1. The square wave output is 24v 200mA. 2. Max load's resistance is 8000 ohm 3. When the load's resistance is decreased,the current will drop to a value but the voltage always keep 24v. I have no idea how to keep 24v.
The frequency must be fixed between 100hZ and 100khZ.
This is not a hardware forum.
Anyway: When the loads resistance is decreased, the current will not drop - it will increase until you reach your rated maximum of 200mA. Then you will have to either shut off the output, or drop the voltage (current regulation) or let the generator burn to cinders.
Your specification only specify "with short circuit protection" so it isn't obvious if it should decrease the voltage or just disconnect the load.
Don't you mean that the frequency must be variable between 100Hz and 100kHz?
Further: You call it a "AC square wave constant voltage generator". Does that mean that it should generate +/- 24V (or maybe +/- 12V), i.e. that it should switch polarity? Switching between 0V and +24V is not AC. It is just pulsed DC.
Finaly: you require 200mA output, but specify max load 8000 ohm. Max load is expected to be the lowest resistance that may be used. 24V / 8000 ohm means 3mA which is way less than 200mA. Did you really mean that the max load should be 8000 ohm or did you mean that the minimum load is 8000 ohm, i.e. that the load may vary between 120 ohm and 8000 ohm?
I may be being dim here, but ...
Doesn't AC stand for Alternating Current? Which would imply alternating (and therefore not constant) voltage.
A constant voltage would normally be referred to as DC.
"Doesn't AC stand for Alternating Current? Which would imply alternating (and therefore not constant) voltage."
Maybe he means constant amplitude?
I don't think it's unusual to speak of a "constant amplitude" AC source as "constant voltage" - even if, as you say, it isn't literally true?
... we could also ask whether this is really AC - ie alternating - or is it just pulsed DC?
ie, does the voltage swing between +24V and -24V (or +/-12V), or is it just 0V and 24V?
Anyway, you don't specify any load regulation for your generator. If you really did mean that max load is 8000 ohm, then you can select a trivial solution.
Just use a 24V linear voltage regulator and feed the 24V to a switch transistor controlled by a logic-level squarevave generator.
Place a 120 ohm resistor between transistor and connector.
Your short-circuit current will then be 24V/120ohm = 200mA.
Your open-circuit voltage will be 24V (minus a little loss in the switch transistor).
Your fully loaded current will be 24V / (120 + 8000) A = 0.00296A.
Your fully loaded volage will be 24V - 24 * 120 / (120 + 8000) V = 23.65V (minus a little loss in the switch transistor).
Your load regulation will be 1.5% which should be good enough for most usages.
But this is only valid if you by 200mA meant short-circuit current, and didn't mean max current at nominal load (which would be 120 ohm and not 8000 ohm).
Additionally
24 V on 800 ohm get 30 mA so you have to check your specification. For 800 ohm load you need at least a generator with 160 V.
For a simple on/off a switched constant current generator can do the job (the frequency can be the problem if too high).
You are an order of magnitude off. The specified load was 8 kohm, not 800 ohm, so it would take 1,6kV to drive 200mA through the load, and the power sent into the load would be 320W at 50% (?) duty cycle.