Quick question on voltage ripple. I built the buck regulator circuit using the MC34063. My circuit is the same as the buck regulator circuit in the datasheet that takes 25V in and outputs ~5V with a 220uH inductor. I use the same diode, same sized caps etc... I wanted to recreate this circuit on my to be sure I understood the concepts i.e ripple voltage, duty cycle, periods etc... It looks like it is working find because I have the expected on times and frequency from the chip with my timing capacitor, but my ripple voltage seems to be excessively high. My output cap has an ESR value of 100m Ohms and the calculated ripple current is something like 0.345 amps. I take [(Vin-Vout)*t_on]/L to get the 0.345 amps. If V_ripple = I_ripple * ESR I should get a ripple voltage of ~34.5mV. When I look at the output on my scope it looks like my ripple voltage is 1V peak to peak. Said another way, my ripple peak goes up to 500mV and down to -500mV (the scope is set on AC coupling since I don't care about the DC component).
Does anyone see what I'm missing here?
I'm also running the the chip fast because I'm using a ~48pF cap for my timing capacitor which gives me a frequency right at 100kHz which I've verified on my O'scope. Everything seems to be adding up except my voltage ripple. I would think that especially since I'm switching faster than the example my circuit should be able to handle more current and have an even lower voltage ripple.
Thanks
Robbie