5

The AQZ262 can switch on and off in less than 10ms. It is specified as 60 AC/DC at 6A. Yet it has a specification of 0.5cps maximimum. Why?

Dirk Bruere
  • 13,723
  • 9
  • 54
  • 115
  • 1
    Possibly due to heating effects. Sure, the AC line frequency may be 60Hz, but when "on" it is just "on." Transitioning from on to off and back, takes time and energy. – rdtsc Apr 12 '16 at 13:25
  • 1
    Perhaps because of the minimum time it needs to recover/reverse from the previous switching? – Eugene Sh. Apr 12 '16 at 13:25
  • 1
    A lot of them have limited switching times due to power dissipation reasons. Why it is for this part, only the manufacturer can tell why they really chose that value and nothing else. – PlasmaHH Apr 12 '16 at 13:27
  • I'm using it at 12VDC, 1.5A switching twice a second. No obvious problems, and not warm to the touch – Dirk Bruere Apr 12 '16 at 13:31
  • Probably it is going to reduce it's life time. – Eugene Sh. Apr 12 '16 at 13:32
  • Since a SSR is a sealed (usually potted) unit, it is impossible to tell the temperature of the components inside. The potting compound is a very effective thermal insulator, so while the bulk current pass elements may not be getting warm from AC current flow, the smaller, discrete control electronics may overheat and be damaged. – rdtsc Apr 12 '16 at 14:16

2 Answers2

7

This is almost definitely for thermal considerations:

From the datasheet tables:AQZ262 data

Note that the maximum frequency has conditions of V\$_L\$(max) and I\$_L\$(max).

There is a handy chart:

AQZ262 Frequency vs load

This shows the maximum operating frequency for various output power loading; for your case (18W total) you should be able to operate at up to 10 cycles per second.

[Update]

The V*I curve above appears to be V(peak) * I(peak) rather than the RMS values more commonly found.

[Update 2]

Spehro made an excellent comment about the MOSFETs spending considerable time partially on, and that is definitely so:

AQZ262 Turn on time vs If

At 10mA forward current, it appears to take almost 5 msec to turn on even at a very modest load.

Peter Smith
  • 22,313
  • 1
  • 29
  • 65
  • 1
    Yes, every time it switches the MOSFETs spend a considerable amount of time partially on, so the heating is much more than if it was just left on or off. Note that your graph is at 25°C Ta- it should presumably be derated considerably to allow a reasonable operating temperature range. – Spehro Pefhany Apr 12 '16 at 13:51
  • An excellent point Spehro; added to answer with graph showing slow turn on times. – Peter Smith Apr 12 '16 at 14:00
2

It's possible that the entry you're looking at is a typo. Note page 628, figure 13 of the data sheet. This suggests a maximum switching rate of about 40 Hz at 6 amps, which is the rated current for your device.

WhatRoughBeast
  • 60,521
  • 2
  • 37
  • 97