I'm new to EE so please go easy.....PSUs are all about 'low noise' and then give us a reading in uV.
Just playing with some regs here....7v ac into a rectified 7085 ....5.015 Vdc but also 0.006vac.
Then fed thru a lm317t and reg to 3.45v. (No load)....and I'm down to 0.004vac.
Is this AC reading the noise or ripple we talk about RE PSUs and are the two things the same?
Brain fart moment whilst tinkering about......spent a couple hours building a 317/337 +- board today.....then fed it mains 240vac....nice one
Magic smoke was released and the RCD shut the house down....silly me. Maybe just fried the regs.
Just playing with some regs here....7v ac into a rectified 7085 ....5.015 Vdc but also 0.006vac.
Then fed thru a lm317t and reg to 3.45v. (No load)....and I'm down to 0.004vac.
Is this AC reading the noise or ripple we talk about RE PSUs and are the two things the same?
Brain fart moment whilst tinkering about......spent a couple hours building a 317/337 +- board today.....then fed it mains 240vac....nice one
Magic smoke was released and the RCD shut the house down....silly me. Maybe just fried the regs.
Hi Jim,
"Ripple" is normally used to describe the variation in voltage caused by periodical operation in a power supply.
For a power supply made up of a transformer, a bridge rectifier and a capacitor bank (energy storage), the ripple is the voltage variation on the capacitor bank from 100HZ (double rectification / Europe) recharging of the capacitor bank. This voltage ripple evidently increases with increasing load current that discharges the capacitor bank in-between the recharging moments.
For an SMPS, the voltage ripple relates to the switching frequency of the SMPS (often 50kHz-200KHz). Sometimes the ripple frequency is the same as the switching frequency, sometimes the ripple frequency is the double (depends on the SMPS design). Again, it relates to voltage variations at a capacitor (or capacitors) in the output of the SMPS.
"Noise" is normally used to describe random voltage variations of a voltage, typically with an almost white noise distribution. Sometimes "noise" is used for the sum of voltage variations as supply voltage variation in general is seen as unwanted.
A stupid question: What is a "rectified 7085"? One reason I ask is that you enter 7Vac and get 5.015Vdc. It sounds a bit strange.
When you measure 0.004Vac (4mV) at the output of an LM317, it is most likely your multimeter that is not precise enough (mine are no better). An LM317 can do some hundreds of micro-Volt of noise.
Why you released smoke I cannot say with this limited information but I normally test a new regulator with some 47 Ohm in series with the regulator input (no load at the output). This way the current is limited and the chance that the smoke is released much less.
"Ripple" is normally used to describe the variation in voltage caused by periodical operation in a power supply.
For a power supply made up of a transformer, a bridge rectifier and a capacitor bank (energy storage), the ripple is the voltage variation on the capacitor bank from 100HZ (double rectification / Europe) recharging of the capacitor bank. This voltage ripple evidently increases with increasing load current that discharges the capacitor bank in-between the recharging moments.
For an SMPS, the voltage ripple relates to the switching frequency of the SMPS (often 50kHz-200KHz). Sometimes the ripple frequency is the same as the switching frequency, sometimes the ripple frequency is the double (depends on the SMPS design). Again, it relates to voltage variations at a capacitor (or capacitors) in the output of the SMPS.
"Noise" is normally used to describe random voltage variations of a voltage, typically with an almost white noise distribution. Sometimes "noise" is used for the sum of voltage variations as supply voltage variation in general is seen as unwanted.
A stupid question: What is a "rectified 7085"? One reason I ask is that you enter 7Vac and get 5.015Vdc. It sounds a bit strange.
When you measure 0.004Vac (4mV) at the output of an LM317, it is most likely your multimeter that is not precise enough (mine are no better). An LM317 can do some hundreds of micro-Volt of noise.
Why you released smoke I cannot say with this limited information but I normally test a new regulator with some 47 Ohm in series with the regulator input (no load at the output). This way the current is limited and the chance that the smoke is released much less.
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Never build, or work on, a circuit without an isolation transformer,
unless it runs on batteries. This was very nearly lethal.
Thanks for the replies and FF for your in depth summary. I have a lot to learn
Sorry I meant 7805....as in i sent 7vac through a rectifier and then into the 7805 regulator....giving the 5.015v.
Rayma thankyou for the concern. I do have the utmost respect for the mains and I always keep clear when powering things up first time. But I heed your advice, thanks.
Sorry I meant 7805....as in i sent 7vac through a rectifier and then into the 7805 regulator....giving the 5.015v.
Rayma thankyou for the concern. I do have the utmost respect for the mains and I always keep clear when powering things up first time. But I heed your advice, thanks.
I assume you did have a transformer between the mains and the regulator since you mention 7Vac?
I always check all my circuit connections with an Ohm-meter before applying power. With many connections, we all make mistakes from time to time. The check with an Ohm-meter reduces the risk of damage considerably.
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